diff --git a/lib/autoconf/headers.m4 b/lib/autoconf/headers.m4
index 8944da41..5cd1f4d5 100644
--- a/lib/autoconf/headers.m4
+++ b/lib/autoconf/headers.m4
@@ -633,8 +633,10 @@ AC_DEFUN([AC_CHECK_HEADER_STDBOOL],
              bool *pp = &p;
 
              /* C 1999 specifies that bool, true, and false are to be
-                macros, but C++ 2011 and later overrule this.  */
-             #if __cplusplus < 201103
+                macros, but C++ 2011 overrules this.  The C++ committee
+                was codifying existing practice, so we allow them to
+                not be macros whenever __cplusplus is defined.  */
+             #ifndef __cplusplus
               #ifndef bool
                #error "bool is not defined"
               #endif
diff --git a/tests/local.at b/tests/local.at
index 3f348929..f79f57ff 100644
--- a/tests/local.at
+++ b/tests/local.at
@@ -593,9 +593,9 @@ AT_CMP([at_defines-$1], [at_defines-$2])[]dnl
 m4_define([_AT_DEFINES_CMP_PRUNE],
 [m4_bmatch([$1],
   [^vary:],
-[	/@%:@define ]m4_bpatsubsts([$1], [\<vary:], [])dnl
+[	/@%:@define ]m4_bpatsubsts([$1], [\<vary:], [])[]dnl
 [@<:@ @{:@@:>@/ d ;@%:@@:}@
-	/@%:@undef ]m4_bpatsubsts([$1], [\<vary:], [])dnl
+	/@%:@undef ]m4_bpatsubsts([$1], [\<vary:], [])[]dnl
 [@<:@ @{:@@:>@/ d ;@%:@@:}@
 ],
   [m4_fatal([unrecognized AT_DEFINES_CMP variance token: "$1"])])])